The pH of brain extracellular fluid in the cat

Abstract

SUMMARY1. The blood supply to the medulla was determined by the injection of indian ink via the vertebral arteries. Virtually the whole medulla was supplied by penetrating vessels from the ventral surface. The highest density of small arterioles and venules was found close to the roots of XII and on the ventrolateral surface.

Central chemosensitivity and the reaction theory.

“…Cragg, Patterson & Purves (1977) did not see increases of ventilation when applying acid to the ventral side of the medulla. It must, however, be stated that the experiment is not easy.…”

“…Recently pH was successfully measured either with micro-electrodes in the tissue of the medulla oblongata (Cragg et al 1977) or with macro-electrodes on the surface of the medulla Ahmad, Berndt & Loeschcke, 1976;Shams, 1981).…”

“…The former technique (Cragg et al 1977) has the advantage that the electrode is in the tissue, and the latter (Ahmad et al 1976) that it is non-invasive. Cragg et al (1977) were able to answer the old question (Lambertsen, Semple, Smith & Gelfand, 1961) as to whether the time courses of the pH in the medullary tissue and of ventilation during CO2 inhalation are compatible. The answer was in the affirmative, indicating that the electrode indeed measures a pH which is representative of the stimulus.…”

Regulation of Ventral Surface Chemoreceptors by the Central Respiratory Pattern Generator

“…The modestly lower pH sensitivity of the neurons in vitro (Ϫ43%) could be attributable to the immaturity of the cells, a slight difference in the sampled population, the incomplete reduction of synaptic inputs by KYN in vivo, or a direct stimulatory effect of halothane. Finally, the changes in arterial pH may underestimate the changes in brain extracellular pH during hypercapnia (Cragg et al, 1977;Eldridge et al, 1984;Kintner et al, 1999;Li and Nattie, 2002) because brain extracellular fluid (ECF), being protein poor unlike blood, may behave more like a bicarbonate buffer (Boron, 2003;Richerson and Boron, 2003).…”

Inspiratory response to occlusion of arteries in the ventral surface of the medulla in anesthetized cats.

“…However, there is still uncertainty about both the actual location and the effective stimulus of the chemosensitive elements, as shown in recent reviews (Millhorn and Eldridge 1986;Bruce and Cherniack 1987). Furthermore, the arterial blood supply to the central chemo receptor has not been studied, although the vascularity of the medulla in cats and rats was described in detail by Cragg et al (1977).…”